The prior art systems for sensing the level of granular materials such as fly ash or grain in bins or hoppers have posed several problems. Thus, for example, it is not always feasible to provide electrical wiring at a hopper site for powering gages or relaying detected indications. Even if feasible, the possibility of explosion in the presence of electrical sparks about the finely divided dust of a grain bin, for example, is a serious problem. Yet it is desirable to communicate as efficiently and directly as possible to electronic monitoring and analysis sytems such as computers, where electrical on-off signals are the preferable form of input.
Even when non-electric sensors are used, for example, air pressure gages, other similarly serious problems occur. If air flow paths need be piped into a hopper or bin this can be even more expensive and inconvenient than electrical circuitry. Also air flow paths can become clogged with silt and dirt, thereby drastically changing calibration and operability characteristics. If a pressure or vacuum air source need be supplied, the prior art sensing systems tend to be critically affected by changes of pressure that occur in the system during flow of materials into or from the hoppers, etc.
A typical prior art air pressure operated hopper content level indicating system is set forth in U.S. Pat. No. 2,640,977 to J. T. Parisi--June 2, 1953.
It is therefore a general object of this invention to improve the state of the art by providing pressure responsive level detector systems for correcting the foregoing prior art deficiencies.